1. Technical Field
The invention relates to tire making equipment and in particular to the curing press in which a green tire is placed and cured through use of an elastomeric inflatable bladder. More particularly, the invention relates to a tire curing press and to a control system therefore which determines whether there is a leak in the tire curing bladder or other portion of the curing fluid supply and exhaust system after each curing cycle, and to the means for preventing the start of the next curing cycle if a leak is detected.
2. Background Information
In the manufacture of pneumatic tires or other elastomeric articles such as air spring bladders, etc., the article is placed into a curing press wherein an inflatable bladder which is supplied with a heated curing fluid expands outwardly and presses the green elastomeric article against the inner surfaces of the mold where it is subsequently heated for a predetermined time until the article cures. After the desired cure has been achieved, appropriate control mechanisms open a drain line to the press which removes the spent curing fluid. This deflates the curing bladder, afterwhich, the mold is open and the cured tire or article removed therefrom. Another green tire or article then is placed in the press for a subsequent curing operation.
During the curing of the article and in particular pneumatic tires, it is critical that the desired curing pressure be maintained in order to properly cure the tire. Occasionally, a leak develops in the bladder and/or fluid inlet and outlet fluid lines causing leaks, which if undetected, result in an ineffective curing of the tire, which is subsequently scrapped after detection, which then indicates that a leak has developed in the system.
Heretofore, several tires would have been produced prior to the leak being detected during the subsequent inspection of the cured tires. This results in several scrap tires being produced as well as resulting in needless expense and time. The defect in the tires is caused by the curing fluid coming into contact with the tire, causing imperfections in the final cured tire.
Prior art leak detection systems generally use pressure actuated switches which were tripped upon detecting an excess amount of steam or water during the load or curing cycle. This requires some clean-up periodically to clean the pressure switch and attached lines so that a free flow of fluid to the pressure switch can be maintained.
Some examples of prior art systems for detecting malfunctions in a tire curing press are shown in the following patents.
U.S. Pat. No. 3,859,015 discloses a device for detecting the shape of a green tire as it is being formed in a tire mold. Fluidic sensors sense the expanding position of the green tire as it is being formed in the mold press. The sensors are triggered and send signals to a control box which will interrupt the flow of steam into the shaping bladder. Also, a warning device will notify the operator if a reversing signal has not been produced which indicates a leaking bladder within the tire press.
U.S. Pat. No. 3,942,922 discloses a tire press and a mold leak control system wherein the pressure of the fluid medium in the tire cavity is continuously monitored. Pressure responsive switches are utilized in conjunction with a gas leak monitoring circuit to monitor the pressure of the fluid medium in the tire cavity. If the pressure falls below a predetermined level, the heating and/or pressure media is terminated and a new tire is prevented from being put into the mold.
U.S. Pat. No. 4,222,721 merely discloses a method and apparatus for purging curing fluid from a bladder in a tire curing press.
U.S. Pat. No. 4,502,857 discloses a continuous monitoring system to determine the pressure within the mold cavity as the green tire expands. A resulting change in air pressure will be directed through a conduit to pressure sensors which determine if the bladder pressure is at the necessary level.
U.S. Pat. No. 4,721,590 discloses a method for determining the amount of time needed to blow down the steam in a tire curing press so that the tire will remain in the press for the shortest time possible. Pressure transducers communicate with the inside of the bladder and are connected to a blow down manifold. During the blow down period, a vacuum is applied to an inlet conduit which will further accelerate the loss of pressure in the bladder. A valve controls a venturi type pump which is connected to the inlet line.
U.S. Pat. No. 4,744,931 discloses the use of a shaping system for green tires having multiple curing presses that have a common exhaust manifold. Pressure transducers sense pressures in the bladders for a plurality of the presses. A programmable controller controls the presses with respect to the signals received in the pressure transducers. This system allows the correct amount of pressure to be determined for the proper curing of the tires within the tire molds.
As discussed above, nearly all of these prior art control systems use the pressure of the curing fluid for controlling the presses and for determining if a leak occurs, whereas the leak detector of the present invention uses the vacuum which is created within the bladder and connected piping during removal of the spent curing fluid for the leak detection means.